1. Field of the Invention
The present invention relates to an electron tube having a linear member, such as a cathode filament, a linear grid, a linear damper for the cathode filament or for the linear grid, and a linear spacer for the cathode filament or for the linear grid. More particularly, the present invention relates to a fixing structure of the linear member in a fluorescent luminous tube, such as a fluorescent display tube in which the linear member is mounted under tension.
2. Description of the Prior Art
A fluorescent display tube, as a kind of a conventional electron tube shown in Japanese Patent Laid-Open Publication No. 2002-245925, will be described with reference to FIGS. 8(a) and 8(b). FIG. 8(a) is a cross-sectional view illustrating a fluorescent display tube taken along the line X2-X2 in FIG. 8(b) looking in the directions of the arrow. FIG. 8(b) is a cross-sectional view illustrating the fluorescent display tube taken along the line X1-X1 in FIG. 8(a) looking in the direction of the arrow.
The fluorescent display tube has a hermetic container formed of substrates 111 and 112 to be opposite to each other, and side plates 121 to 124. The hermetic container contains filaments 23, a grid 33, and an anode electrode 31 therein. Electrons emitted from the filaments 23 are controlled by the grid 33 to reach the anode electrode 31, and the reached electrons excite fluorescent material on the anode electrode 31 to make the fluorescent material emit light.
A pair of aluminum (Al) thin films 211 and 212 for use as a cathode electrode is formed on the substrate 111. The ends of the filament 23 are held between the Al thin film 211 and an Al wire 251, and the Al thin film 212 and the Al wire 252, and bonded to the Al thin films 211 and 212 and the Al wires 251 and 252 by ultrasonic bonding. Spacers 261 and 262 made of an Al wire sustain the filament 23 at a predetermined elevated height.
The conventional fluorescent display tube shown in FIGS. 8(a) and 8(b) requires to dispose therein the filament 23 having both side ends thereof fixed between the Al thin film 211 and the Al wire 251 and the Al thin film 212 and the Al wire 252 respectively, as well as the spacers 261 and 262 for sustaining the filament 23 at the predetermined elevated height. This results in increasing dead space in the fluorescent display tube, and is obstructive to reduce the size of the fluorescent display tube.
Moreover, the filament 23 merely touches the spacers 261 and 262 and are not fixed to the spacers 261 and 262. Thus, the filament 23 is liable to sideslip in the lengthwise directions of the spacers 261 and 262 while the fluorescent display tube is being assembled or being used. The sideslip changes the light emission of the fluorescent material on the anode electrodes 31 and deteriorates the display quality of the fluorescent display tube.
The conventional fluorescent display tube separately arranges the Al wires 251 and 252 for fixing the filaments 23, and the spacers 261 and 262 for sustaining the filaments 23 at the predetermined elevated height. In other words, the conventional fluorescent display tube requires the Al wires 251 and 252 for fixing the filaments 23, and the Al spacer wires 261 and 262.